\documentclass{article}
\usepackage[pdftex,active,tightpage]{preview}
\setlength\PreviewBorder{2mm}
\usepackage{tikz}
\usetikzlibrary{arrows,positioning,fit,shapes}

\begin{document}
\begin{preview}
\begin{tikzpicture}[scale=1,node distance=2.0cm]
  \node (Phi) at (0,0) {$\Phi: V$};
  \node (W)  [right of=Phi] {$W$};
  \node (Kn) [below of=Phi] {$K^n$};
  \node (Km) [right of=Kn]{$K^m$};
  \node[text=green]  (TN) at (1,0.7)  {Koordinatenfrei};
  \node[text=orange] (TS) at (1,-2.6) {Konkretes Rechnen};
  \draw[->, above] (Phi) to node {$\Theta_B$} (W);
  \draw[->, below] (Kn)  to node {$\Theta_{B'}$} (Km);
  \draw[->, left] (Phi)  to node {$\Theta_B$} (Kn);
  \draw[->, right] (W)   to node {$\Theta_{B'}$} (Km);
  \node [ellipse,fit={(Kn) (Km) (TS)}, draw=orange, thick, text=orange]
        {};
  \node [ellipse,fit={(Phi) (W) (TN)}, draw=green, thick, text=green]
        {};
\end{tikzpicture}
\end{preview}
\end{document}
